Hydraulic expansion chuck and method for producing such an expansion chuck

ABSTRACT

A hydraulic expansion chuck includes a basic body, an expansion bush which is received in the basic body and defines a reception space for a tool to be clamped, and a pressure chamber which is delimited between the expansion bush and the basic body. A securing pin is provided, which extends through the basic body and the expansion bush into the reception space. A method for producing a hydraulic expansion chuck is disclosed. First, a basic body is provided with a blind hole, into which an internal thread is cut. Then, an expansion bush is soldered into the basic body. Finally, an orifice is made at the bottom of the blind hole and extends through the material of the expansion bush into a tool reception space which is delimited in the expansion bush.

FIELD OF THE INVENTION

The invention relates to a hydraulic expansion chuck with a basic body,with an expansion bush which is received in the basic body and defines areception space for a tool to be clamped, and with a pressure chamberwhich is delimited between the expansion bush and the basic body. Theinvention relates, furthermore, to a method for producing a hydraulicexpansion chuck.

BACKGROUND OF THE INVENTION

Hydraulic expansion chucks are generally known. A shank of a tool to beclamped can be inserted into the reception space. The pressure chamberis then put under pressure, with the result that the expansion bush isforced against the shank of the tool. The shank of the tool is then heldfrictionally in the reception space.

When the tool received in the expansion chuck is used for roughingmachining tasks, high torques have to be transmitted between theexpansion chuck and the tool. If the maximum holding moment of theexpansion chuck is in this case overshot, relative movements occurbetween the tool and the expansion chuck. This may ultimately causedamage to the tool.

SUMMARY OF THE INVENTION

The object of the invention is to provide an expansion chuck, by meansof which high torques can be transmitted reliably to the tool. Theobject of the invention is, furthermore, to provide a method forproducing such an expansion chuck.

To achieve this object, according to the invention, in a hydraulicexpansion chuck of the type initially mentioned, a securing pin isprovided, which extends through the basic body and the expansion bushinto the reception space. The securing pin can engage into a groovewhich is provided on the shank of the tool to be received. Thus, inaddition to the frictional connection, a positive connection is achievedbetween the expansion bush and the tool shank, so that the tool cannotrotate in the reception space even under high loads. The expansion chuckaccording to the invention is in this case based on the recognition thatthe functioning of the expansion chuck can be maintained even though thesecuring pin extends through the expansion bush. It is also possible forthe reception space to receive tools which have no groove which is tointeract with the securing pin. Such a tool is pushed with its shankinto the reception space until the end face of the shank bears againstthe securing pin. The shank is then clamped in the expansion chuck inthe conventional way, to be precise solely by means of a frictionalconnection.

Preferably, a plurality of securing pins are provided, which arearranged so as to be spaced apart uniformly from one another in thecircumferential direction. This causes force to be introduced uniformlyalong the circumference of the shank of the tool received in thereception space. In particular, three securing pins may be used, whichare arranged at an angular interval of 120° in relation to one another.

Preferably, there is provision whereby the expansion bush has a solderportion, in the region of which it is soldered to the basic body, andwhereby the securing pin extends through the solder portion. Thisrefinement affords two advantages. On the one hand, the securing pin isarranged outside the pressure chamber which is delimited between thebush and basic body. This ensures that the use of the securing pin doesnot lead to any leaktightness problems. On the other hand, the securingpin, when located in the region of the solder portion, is arranged inproximity to the inner end of the reception space. A long clampingregion therefore remains for those tools which are not provided on theshank with a groove into which the securing pin is to engage.

Preferably, there is provision whereby the securing pin has a threadedportion and a pin portion, the diameter of the pin portion being smallerthan the diameter of the threaded portion. The pin portion, since it isthreadless, can be received reliably in the orifice extending throughthe expansion bush and can fix the tool firmly against rotation.

According to the invention, a method for producing a hydraulic expansionchuck is also provided, in which, first, a basic body is provided with ablind hole, into which an internal thread is cut. An expansion bush isthen soldered into the basic body. An orifice is subsequently made atthe bottom of the blind hole and extends through the material of theexpansion bush into a tool reception space which is delimited in theexpansion bush. The basic concept of this method is that the receptaclefor the securing pin is produced in two steps. In the first step, anorifice is provided which is given an internal thread. In the secondstep, an orifice is made which connects the portion provided with theinternal thread to the reception space for the tool. In this case, thesecond part of the receptacle is produced after the expansion bush hasbeen soldered to the basic body. Two advantages are thereby afforded: onthe one hand, that region of the expansion bush through which thesecuring pin subsequently extends is closed during soldering, so that nosolder material can flow out in an undesirable way. On the other hand,the material quantity which has to be removed after soldering in orderto finish the receptacle for the securing pin is minimized. Since theexpansion chuck is usually also hardened at the same time as theexpansion bush is soldered in, drilling would otherwise have to becarried out in hardened material and, above all, an internal thread cut.

Preferably, the orifice is drilled through the expansion bush. Thisresults in a low outlay in production terms.

According to an advantageous refinement of the invention, a butt plug isintroduced into the reception space, and at least one securing pin isscrewed into the internal thread in the basic body until the securingpin bears against the butt plug. The butt plug makes it possible to setthe correct screw-in depth of the securing pin at low outlay.

Preferably, in this case, there is provision whereby the securing pin,when it is screwed in correctly, is secured by a screw securing means,in particular based on an adhesive. This ensures that the securing pinis not undesirably shifted out of place when the expansion chuck is usedlater.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described below by means of an embodiment illustratedin the accompanying drawings in which:

FIGS. 1 a to 1 c show a side view, a front view and a sectional view ofan expansion chuck according to the invention in a first state ofmanufacture;

FIG. 2 shows a sectional view of the expansion chuck from FIG. 1 in asecond state of manufacture;

FIG. 3 shows a sectional view of the expansion chuck after manufactureis concluded; and

FIG. 4 shows the expansion chuck according to the invention with aninserted tool shank.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 a to 1 c show an expansion chuck 10 which has a machinetool-side end 12 and a tool reception-side end 14. The expansion chuck10 has a basic body 16, which is composed of metal, and an expansionbush 18, likewise composed of metal. Inside the expansion bush 18, areception space 20 is formed, which issues on the tool reception-sideend face of the expansion chuck 10.

The essential feature of the expansion chuck is that it is provided witha plurality of securing pins which are intended to interact with a toolreceived in the reception space 20, more precisely with grooves whichare provided on the tool shank. These securing pins are received inreceptacles which are provided in each case as a stepped bore in thebasic body 16 and the expansion bush 18.

FIGS. 1 a to 1 c show the expansion chuck in a first intermediate stateduring production. This intermediate state is distinguished, inparticular, in that a blind hole 22, which is given an internal thread24, is provided for a securing pin in the basic body 16 for eachreceptacle to be produced later. The blind hole, on the one hand, isdesigned to have a depth such that the internal thread 24 has sufficientaxial length. On the other hand, the blind hole 22 ends at a sufficientdistance from the inner space, into which the expansion bush 18 isinserted, in the basic body 16.

The expansion bush 18 inserted into the basic body 16 can be seenclearly in FIG. 1 c. The expansion bush 18 has at its two axial endsportions where it is to be soldered to the basic body 16. These are, atthe inner end, a ring-shaped solder portion 26 and, at the outer end, astepped solder portion which is composed of a radially oriented annularsurface 28 and of an annular surface 30 adjoining the latter and runningin the circumferential direction. Delimited between the solder portions26 and 28, 30 is a pressure chamber 32 which can be supplied with ahydraulic fluid through ducts (not shown here).

The expansion bush 18 is soldered to the basic body 16 in the stateshown in FIG. 1, that is to say in a state in which that portion in thebasic body 16 which is assigned to the solder portion 26 of theexpansion bush 18 is closed in the circumferential direction. Thisensures that no solder material can escape in this region out of the gaparound the solder portion 26.

When the expansion bush 18 is being soldered into the basic body 16, atemperature/time profile such that the expansion chuck overall ishardened is usually employed.

FIG. 2 shows the expansion chuck in a state in which, after thesoldering of the expansion bush 18 to the basic body 16, an orifice 34has been formed at the bottom of the blind hole 22. The orifice 34 ismade, in particular, as a bore and connects the space provided with theinternal thread 24 to the reception space 20 inside the expansion bush.Thus, overall, the earlier blind hole 22 has given rise to a steppedbore, the portions 22, 34 of which together form a receptacle 35 for asecuring pin. The orifice 34 is in this case formed concentrically withthe internal thread 24 and passes through the expansion bush 18 in thesolder portion 26. The orifice 34 is therefore surrounded on all sidesby the solder material in the region of transition from the basic body16 to the expansion bush 18 and is located at a distance from thepressure chamber 32. There are therefore no sealing problems.

FIG. 3 shows the expansion chuck 10 in a fully assembled state in whicha securing pin 36 is screwed into the receptacle 35. The securing pin 36is composed of a threaded portion 38 and of a pin portion 40. Thethreaded portion 38 is screwed into the internal thread 24 of thereceptacle 35, and the pin portion 40 extends through the orifice 34 inthe basic body 16 and through the expansion bush 18 in the region of thesolder portion 26. In this case, the outside diameter of the pin portion40 corresponds essentially to the inside diameter of the orifice 34, sothat the securing pin 36 is guided, essentially free of play, in thisregion.

The pin portion 40 of the securing pin 36 extends into the receptionspace 20. In other words, the front inner end of the securing pin 36projects inward beyond the inner wall of the expansion bush 18. In orderto determine at low outlay the desired correct screw-in depth of all thesecuring pins 36, a butt plug 50 may be used, which has a guide portion52 and a butt portion 54. The guide portion 52 serves for guiding thebutt plug 50, free of play, inside the reception space 20. The buttportion 54 has a smaller diameter than the guide portion 52 and servesfor limiting the screw-in depth of the securing pins 36. The securingpins 36 are screwed into the internal threads 24 until their front endsbear against the butt portion 54 of the butt plug 50. They can besecured in this position by a screw securing means, in particular by anadhesive.

FIG. 4 shows a shank 60 of a tool, not illustrated in any more detailhere, which is clamped in the reception space 20 of the expansion chuck.The insertion depth is determined by an adjustable buttress pin 62, andthe securing pin 36 (or, more precisely, the overall three securingpins; see the three receptacles 35 in FIG. 1 b) engage in each case intoa groove 64 which is provided at the rear end of the shank 60. Apositive connection effective in the circumferential direction isthereby implemented by the mechanical engagement of the securing pins 36into the grooves 64.

1. A hydraulic expansion chuck with a basic body, with an expansion bushwhich is received in the basic body and defines a reception space for atool to be clamped, and with a pressure chamber which is delimitedbetween the expansion bush and the basic body, wherein a securing pin isprovided, which extends through the basic body and the expansion bushinto the reception space.
 2. The expansion chuck as claimed in claim 1,wherein a plurality of securing pins are provided, which are arranged soas to be spaced apart from one another uniformly in the circumferentialdirection.
 3. The expansion chuck as claimed in claim 1, wherein theexpansion bush has a solder portion, in the region of which it issoldered to the basic body, and wherein the securing pin extends throughthe solder portion.
 4. The expansion chuck as claimed in claim 1,wherein the securing pin has a threaded portion and a pin portion, thediameter of the pin portion being smaller than the diameter of thethreaded portion.
 5. A method for producing a hydraulic expansion chuckby means of the following steps: providing a basic body with a blindhole, into which an internal thread is cut, soldering an expansion bushinto the basic body, providing an orifice at the bottom of the blindhole and extends through the material of the expansion bush into areception space for a tool to be clamped which is delimited in theexpansion bush.
 6. The method as claimed in claim 5, wherein the basicbody and the expansion bush are hardened during soldering.
 7. The methodas claimed in claim 5, wherein the orifice is drilled.
 8. The method asclaimed in claim 5, further comprising introducing a butt plug into thereception space, and screwing at least one securing pin into theinternal thread in the basic body until the securing pin bears againstthe butt plug.
 9. The method as claimed in claim 8, wherein the securingpin is secured by a screw securing means comprising an adhesive.